Description from Flora of China
Aquatic perennials. Culms long, decumbent, spongy, rooting at lower nodes, internodes solid, filled with aerenchyma. Leaf blades linear or broadly linear. Inflorescence usually a cylindrical spikelike panicle, rarely with spreading primary branches. Spikelets lanceolate, dorsally compressed, veins prominent, florets 2; lower glume usually about 1/3 spikelet length, base clasping; upper glume shorter than or subequaling spikelet, 5-veined; lower lemma as long as spikelet, 5-veined, apex acute to shortly awned; lower palea absent or much reduced; upper lemma membranous, rarely thinly cartilaginous, smooth, margins hyaline, gripping edges of palea below but free toward apex, apex acute.
Hymenachne is a genus of swamp grasses similar to Sacciolepis, and both are segregates from the large genus Panicum. The culms of Sac-ciolepis are hollow, but in Hymenachne they are filled with aerenchyma.
Five species: tropics of the Old World and New World; three species (one endemic) in China.
(Authors: Chen Shouliang (陈守良); Sylvia M. Phillips)